Many of presently existing mobile networks, as well as possibly future telecommunication networks being defined by standardisation bodies, require end-users with respective user equipments being serviced by serving call control servers of said telecommunication networks. In this respect, when a user attaches to an exemplary telecommunication network operating in accordance with an IP Multimedia Subsystem (IMS), as defined by 3GPP and 3GPP2 standards, by explicitly registering in the telecommunication network, a specific serving call control server is assigned by the network for servicing the user, or rather the user equipment. For the sake of simplicity, both user and user equipment share a same abbreviation “UE” and reference throughout the present specification and drawings.
The assignment of a serving call control server is performed by another entity of the telecommunication network in view of a list of capabilities required in order to fit a number of information elements in a user profile for the user. Said another entity is preferably an intermediate server to be consulted about the user by an access server where the user accesses the telecommunication network through.
At present, in a currently existing architecture for the above IP Multimedia Subsystem (hereinafter referred to as IMS) specified by the 3rd Generation Partnership Project (3GPP), a user (UE) accesses the IMS through a Proxy Call State Control Function (P-CSCF) that asks an Interrogating Call State Control Function (I-CSCF) about the user. The latter consults with a Home Subscriber Server (HSS) in order to obtain a user profile for the user including a number of information elements that serve as criteria for assigning one or another Serving Call State Control Function (S-CSCF), namely the one which offers a required set of specific capabilities for servicing the user (UE).
Apart from the above Call State Control Function entities (P-CSCF, I-CSCF, S-CSCF), an IMS likely includes a plurality of Application Servers (AS) for offering dedicated services to the user. The interactions between the IMS entities and the Application Servers (AS) are governed by triggers, which act on signalling of a Session Initiation Protocol (SIP). Such triggers are part of the user profile stored in the Home Subscriber Server (HSS) and are downloaded to the Serving Call State Control Function (S-CSCF) during a SIP registration of the user (UE). Moreover, such triggers determine the specific Application Server (AS) where a SIP message has to be forwarded when the trigger conditions are met.
In short, the user profile generally comprises a number of information elements wherein a portion thereof represents a set of capabilities that a Serving Call State Control Function entity (S-CSCF) should mostly fulfil for being assigned to the user (UE), whereas another portion thereof represents a set of triggers that the Serving Call State Control Function entity (S-CSCF) applies to determine a specific Application Server (AS) for offering a dedicated service to the user. Moreover, a user profile may include as well another portion of information elements representing authorization for certain services, such as a list of so-called “codec” authorized for the user. Furthermore, a user profile might also include another portion of information elements utilizable for charging and other purposes. In principle, there is no reason to preclude that any of these information elements is utilizable for more than one of the above purposes. More particularly, the user profile may include standardized information elements, namely well-known structured or unstructured elements, as well as proprietary or non-standard information elements of a different nature.
Under currently applicable specifications for IMS, the user profile may be submitted from the Home Subscriber Server (HSS) to the Serving Call State Control Function entity (S-CSCF) upon initiative taken either by the former or by the latter. In a first scenario, for instance, when a user profile is updated in the Home Subscriber Server (HSS) by the telecommunication network operator, for example by adding or deleting triggers, the Home Subscriber Server (HSS) pushes towards the Serving Call State Control Function entity (S-CSCF) a download of the user profile. In a second scenario, also for instance, when a user has been assigned a Serving Call State Control Function entity (S-CSCF) by the Interrogating Call State Control Function entity (I-CSCF), the former requests towards the Home Subscriber Server (HSS) a download of a user profile for the user.
Thus, in an exemplary telecommunication network operating in accordance with an IP Multimedia Subsystem (IMS) for the purpose of the present invention, a user (UE) accesses the network through an access server, namely a proxy call control server (P-CSCF) in this instant specification. The proxy call control server (P-CSCF) communicates with an intermediate network server (I-CSCF) that is coupled with a subscriber server (HSS), the latter being in charge of a user profile for the user. The intermediate network server (1-CSCF) selects an appropriate serving call control server (S-CSCF) for servicing the user based on server capabilities derivable from information elements included in the user profile, and assigns said serving call control server (S-CSCF) to the user. Then, the assigned serving call control server (S-CSCF) requests a download of the user profile to the subscriber server (HSS) coupled with the intermediate network server (I-CSCF).
At present, within the above mechanism as well as when the subscriber server (HSS) pushes on its own the download of the user profile, the serving call control server (S-CSCF) can only either accept the contents of the user profile as they are, or reject both the user profile and servicing to the user. In particular, and taking into account that a user profile may include proprietary or non-standard information elements, a serving call control server (S-CSCF) might under some circumstances accept the user profile with non-understandable information elements, and might present an unexpected behaviour without the operator being aware of. In this respect, there is almost no difference on whether the download of the user profile has been pushed by the subscriber server (HSS) on its own, or requested by the serving call control server (S-CSCF).
For example, a user (UE) might have accessed the telecommunication network through a proxy call control server (P-CSCF), and be assigned a serving call control server (S-CSCF) suitable for fitting the capabilities required for servicing the user accordingly with information elements in a user profile for that user. At a certain time the user might be served by a specific Application Server (AS) offering the user an upgrade of the user's terminal by downloading some software prepared to this end. As a result of this download the subscriber server (HSS) in charge of user profiles is informed and some information elements in the user profile for the user are accordingly updated. The subscriber server (HSS) pushes on its own a download of the updated user profile towards the serving call control server (S-CSCF) currently assigned for servicing the user. The new or updated user profile is analyzed by the serving call control server (S-CSCF) and, provided that any information element is not understood or not supported, said serving call control server (S-CSCF) may either reject the user profile, or follow a “best effort” practice in order to service the user in the best possible manner. As rejecting the user profile, the subscriber server (HSS) may assume that another serving call control server (S-CSCF) should likely be selected, however, the subscriber server may be not fully aware of what new capabilities should be included as selection criteria. On the other hand, when the “best effort” practice is followed by the serving call control server (S-CSCF) the situation is even worse since the subscriber server (HSS) does not even know about a misleading behaviour at said serving call control server (S-CSCF).
In this exemplary scenario, the subscriber server might try to select another serving call control server (S-CSCF), at least when the user profile is rejected, based on the updated information elements that had resulted from the upgrading download carried out by the user. Therefore, upon selection of a second serving call control server (S-CSCF-2), a handover between a previously assigned first serving call control server (S-CSCF-1) and the more suitable second serving call control server (S-CSCF-2) is carried out by de-registering the first serving call control server (S-CSCF-1) while finishing all ongoing sessions in said first serving call control server (S-CSCF-1), and registering the second serving call control server (S-CSCF-2).
This de-registration followed by a new registration of a serving call control server (S-CSCF) is accompanied by a forced termination of ongoing sessions. This procedure may be regarded as a weak network response and a drawback that the present invention is aimed to solve.
Thereby, an object of the present invention is the provision of means and method to improve the currently existing handover between a first and a second serving call control servers in order to better fit the required server capabilities for servicing a user.
In a second exemplary scenario where a first serving call control server (S-CSCF-1) has been selected and assigned for a user, this assigned first serving call control server (S-CSCF-1) requests the download of the user profile to the subscriber server (HSS) as already commented above. Provided that there is any network configuration trouble, the assigned first serving call control server (S-CSCF-1) might encounter unsupported or non-understandable information elements that make it reject the user profile. In this situation, the subscriber server (HSS) has no means to establish new selection criteria for selecting and assigning a second serving call control server (S-CSCF-2) other than the previous ones that addressed the first serving call control server (S-CSCF-1), and which is now found unsuitable.
Therefore, a further object of the present invention is the provision of a mechanism whereby the subscriber server may upgrade the selection criteria for assigning a serving call control server.